Field of the Invention
The present invention refers to an aerial system, in particular a turntable ladder system, according to the preamble of claim 1.
State of the Art
Turntable ladder systems are mounted on top of rescue vehicles, especially fire fighting vehicles. Turntable ladder systems represent one type of aerial system that is equipped with a telescopic ladder, and although the following description may refer to aspects of turntable ladders, the present invention is applicable to other aerial systems comprising extendable ladders or telescopic arms that can be extended to reach remote points at great heights. To further improve the flexibility of such ladders, an articulated arm is added at their end that can be bent downwardly. By this construction it is possible to move the end of the ladder down to the ground to facilitate the access to the ladder, in particular to a cage that may be mounted to the ladder end. This means that the ladder may be accessed not only from the deck of the rescue vehicle but also from the ground in the vicinity of the vehicle.
Preferably, the end of the arm may be lowered while the ladder is in any position, including bending down the arm to the ground in front of the driver's cabin, which will be designated as “bending movement” in the following for the sake of simplicity. Usually the movement of the ladder is controlled from a main operator stand that is located at the base of the ladder, or near its turning axis on top of the vehicle. In this case the driver's cabin blocks the view of the ladder operator so that it is impossible to monitor the ground area in front of the vehicle where the end of the arm shall be positioned during and after the aforesaid bending movement. For this reason, organizations have placed severe administrative restrictions on the operation of such ladders, forbidding movements of ladder parts in areas that cannot directly be monitored from the main operator stand. Under all circumstances injury to any persons present in the area in front of the driver's cabin which could be hurt by a collision with the arm, or objects with which the arm could collide must be avoided.
A similar problem arises when the bending movement of the ladder is operated from an auxiliary operator stand that can be located in a cage at the end of the ladder. The operator of this auxiliary operator stand may not be able to monitor the ground area completely, and there might be obstacles or persons beneath the cage or at his back that can collide with the cage.